A young female patient suffered for 4 months from a widespread erythrodermic rash of unknown origin, marked by a peculiar hyperaesthesia. Haematological and biopsy findings were initially non-specific. A rapid deterioration, accompanied by infiltration of the skin, lymphadenopathy and hepatosplenomegaly was suggestive of Sezary syndrome, which was confirmed by finding of 40% of the lymphocytes being atypical (Sezary cells).